The Nebular Properties of Star-forming Galaxies at Intermediate Redshift from the Large Early Galaxy Astrophysics Census

Publications

Jul 27, 2022·

Jakob M. Helton

Allison L. Strom

Jenny E. Greene

Rachel Bezanson

Rachael Beaton

Cite DOI ADS Pre-Print Publication

$The stellar mass–excitation diagram (MEx). The primary sample of {{< math >}}$0.6 < z < 1.0${{< /math >}} LEGA-C galaxies from Section 2.1.1 is shown with the purple circles. The subsample of LEGA-C galaxies from Section 2.1.2 with observed-NIR spectra from MOSFIRE or FIRE is shown with the cyan circles. LEGA-C galaxies with {{< math >}}$3\sigma${{< /math >}} lower (upper) limits on O3 are shown with the dark purple upward-facing (downward-facing) triangles. The low-redshift comparison sample of {{< math >}}$z \sim 0${{< /math >}} SDSS galaxies from Section 2.2.1 is shown in gray scale with an orange contour, where the contour encloses roughly {{< math >}}$90\%${{< /math >}} of the low-redshift sample. The intermediate-redshift comparison sample of {{< math >}}$z \sim 1.6${{< /math >}} FMOS-COSMOS galaxies from Section 2.2.2 is shown with the blue hexagons and blue line, where the line represents the best-fit linear relation to the FMOS-COSMOS sample. The high-redshift comparison sample of {{< math >}}$z \sim 2${{< /math >}} KBSS galaxies from Section 2.2.3 is shown with the green diamonds and green line, where the line represents the best-fit linear relation to the KBSS sample. The division between {{< math >}}$z = 0.7${{< /math >}} star-forming/composite galaxies and AGNs from Juneau et al. (2014) is given by the black dashed line. The black dotted vertical lines indicate the {{< math >}}$M_{\ast}${{< /math >}} bins that are used throughout. We see that the {{< math >}}$0.6 < z < 1.0${{< /math >}} LEGA-C galaxies appear much more similar to the {{< math >}}$z \sim 0${{< /math >}} SDSS galaxies than the {{< math >}}$z \sim 1.6${{< /math >}} FMOS-COSMOS galaxies and the {{< math >}}$z \sim 2${{< /math >}} KBSS galaxies.$ Figure 4 from Helton et al. (2022, ApJ, 934, 81).

Abstract

We present a detailed study of the partial rest-optical ($\lambda_{\mathrm{obs}} \approx 3600-5600\ \mathrm{\AA}$ ) spectra of $N = 767$ star-forming galaxies at $0.6 < z < 1.0$ from the Large Early Galaxy Astrophysics Census (LEGA-C). We compare this sample with low-redshift ($z \sim 0$ ) galaxies from the Sloan Digital Sky Survey (SDSS), intermediate-redshift ($z \sim 1.6$ ) galaxies from the Fiber Multi-Object Spectrograph (FMOS)-COSMOS Survey, and high-redshift ($z \sim 2$ ) galaxies from the Keck Baryonic Structure Survey (KBSS). At a look-back time of $6-8\ \mathrm{Gyr}$ , galaxies with stellar masses $\mathrm{log}_{10}(M_{\ast}/M_{\odot}) > 10.50$ appear remarkably similar to $z \sim 0$ galaxies in terms of their nebular excitation, as measured using $\mathrm{[OIII]}\lambda5008/\mathrm{H}\beta$ . There is some evidence that $0.6 < z < 1.0$ galaxies with lower $M_{\ast}$ have higher $\mathrm{[OIII]}\lambda5008/\mathrm{H}\beta$ than $z \sim 0$ galaxies and are more similar to less evolved $z \sim 1.6$ and $z \sim 2$ galaxies, which are offset from the $z \sim 0$ locus at all $M_{\ast}$ . We explore the impact of selection effects, contributions from active galactic nuclei, and variations in physical conditions (ionization parameter and gas-phase oxygen abundance) on the apparent distribution of $\mathrm{[OIII]}\lambda5008/\mathrm{H}\beta$ and find somewhat higher ionization in $0.6 < z < 1.0$ galaxies with lower $M_{\ast}$ relative to $z \sim 0$ galaxies. We use new near-infrared spectroscopic observations of a subsample of LEGA-C galaxies to investigate other probes of enrichment and excitation. Our analysis demonstrates the importance of obtaining complete rest-optical spectra of galaxies in order to disentangle these effects.

Type

Journal article

Publication

The Astrophysical Journal, Volume 934, Issue 1, id.81, 18 pages